You'll need to take a look at the Q2A database schema. You can see the schema in qa-db-install.php, or run a test install and look at the database in phpMyAdmin.
Then you'll need to figure out how the tables match up and insert data from one into the other.
Finally you'll need to use the buttons in Admin > Stats to recalculate and reindex all the content.
The hardest part is going to be the users table. Q2A uses sha1 with salt for the passwords - I don't know what phpMyFaq uses but you'll probably need to auto generate passwords for everyone.
